The present invention relates to a power distribution method and a power distribution control apparatus for vehicles.
A standby four-wheel drive system is known in the art. The standby four-wheel drive system controls distribution of power to the front wheels and the rear wheels according to the driving state of a vehicle. When all the four wheels of a four-wheel drive vehicle are being driven, some of the power generated by the engine is transmitted to the rear wheels by a transmission apparatus, which is capable of changing the power distribution ratio to the front wheels and the rear wheels.
A typical transmission apparatus includes an electromagnetic clutch mechanism of a multi-plate wet type. The frictional force among the clutch disks of the electromagnetic clutch mechanism is varied in accordance with the amount of the current supplied to a magnet coil. As the frictional force is increased, the ratio of the power distribution to the rear wheels is increased.
When the power distribution to the rear wheels is increased, the load on the transfer located between the engine and the transmission apparatus, and the load on the rear differential located between the transmission apparatus and the rear wheels are increased. Accordingly, the temperature of the oil lubricating the transfer and the temperature of the oil lubricating the rear differential are likely to increase. When excessively heated, the lubrication performance of the lubricating oil deteriorates.
Accordingly, it is an objective of the present invention to prevent excessive temperature increases at a part that is heated as the ratio of power distribution to vehicle rear wheels is increased.
To achieve the above objects, one aspect of the present invention provides a method for distributing power of a vehicle. The vehicle has a transmission apparatus that changes the distribution ratio of power transmitted from a power source to a plurality of wheels. The method includes detecting the temperature of a part located on a power transmission path between the power source and a wheel to which power is transmitted from the power source through the transmission apparatus, the heat of the part being increased as the power distribution ratio is increased; determining that the current state is a specific state in which the detected temperature reaches a previously set first reference temperature; and controlling the transmission apparatus to lower the power distribution ratio to the wheel from the transmission apparatus when the current state is determined to the specified state.
Another aspect of the present invention provides a power distribution control apparatus for a vehicle. The control apparatus includes a transmission apparatus that changes the distribution ratio of power transmitted from a power source to a plurality of wheels. The control apparatus has a detector and an electronic control unit. The detector detects the temperature of a part located on a power transmission path between the power source and a wheel to which power is transmitted from the power source through the transmission apparatus, the heat of the part being increased as the power distribution ratio at the transmission apparatus is increased. The control unit controls the power distribution ratio at the transmission apparatus thereby controlling the distribution ratio of power to the wheels. When the current state is a specific state in which the temperature detected by the detector is equal to or higher that a previously set first reference temperature, the control unit controls the transmission apparatus to decrease the power distribution ratio.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.